The Schema can be understood as the structure of a data table. With the schema of a certain table, the user will be able to learn the following extremely useful information about the table without seeing a single record.
It is important to know with regards to data transformation that while the schema of the table remains unchanged, all transformation steps defined should stay intact and valid regardless of data update. However any slight change in table schema (such as renaming a single field) can easily cause failure or error in data transformation because the original table is no longer “recognizable”.